The present invention relates to new compositions capable of being composted.
Composts are prepared by a process (called "composting") which is a biological decomposition and stabilization of putrescible organic substrates, more particularly wastes. This process is now used on an industrial scale; it requires low investments and is effective in converting organic wastes to valuable products which can be used for fertilizing purposes and also as a mulch to provide temporary protection of a soil surface against erosion by wind or water.
Since waste having a moisture level less than about 50-60 wt % is more valuable for the production of energy (e.g. by incineration, pyrolysis or the like), organic wastes which are available for composting generally have a high water content. However, problems are often encountered in managing these materials since the presence of large amounts of water may reduce composting temperatures, resulting in inefficient operation and difficulties in composting.
It is a primary purpose of this invention to provide composting compositions from wastes which may have a high moisture level. It is also an object of this invention to provide compositions which are easily converted to composts having a high nutrient content.
According to the present invention, the composting compositions contain essentially:
(a) 95 to 75 wt % of a biomass consisting in particles of residues of the wood industry optionally in admixture with organic wastes, and PA1 (b) 5 to 25 wt % of petroleum sludge.
It has been found that the incorporation of petroleum sludge into the biomass improves the microbiological activity of the mixture and increases the nitrate content of the compost. The petroleum sludges which settle on the bottom of a crude petroleum oil tank or a heavy oil tank in refineries do not need to be previously dewatered. In fact, sludges wherein the water content may reach about 70 wt. % may be incorporated in the composting compositions.
The microbiological activity of these compositions is improved when the amount of petroleum sludge is even as low as 5 wt %. On the other hand, the oligoelements content of the final composts prepared from compositions containing more than 30 wt % petroleum sludge may exceed the maximum amounts specified in FAO regulations. Composting compositions containing from 5 to about 25% petroleum sludges are preferably used. In some cases, and more particularly when the water content of the composting composition is high, it may be advantageous to use an amount of petroleum sludge which does not exceed about 15 wt %.
According to the present invention, the petroleum sludges are incorporated in a biomass consisting in residues of the wood industry, optionally in admixture with organic wastes generally used for producing composts. It has been found that the residues of the wood industry and more particularly sawdust, wood chips, particles of tree barks, tree trimmings and the like, promote the biological decomposition of the composting mixture. They provide structural support and improve the aeration of the mixture.
The biomass may also contain other organic wastes, such as sludges from municipal and industrial wastewater treatment, animal manures and/or wastes from industrial processes, e.g. from the textile industry, the food industry, and the pulp and paper industry. The selection of the waste depends upon its availability and its price, since the waste has to be collected and transported to the composting installation.
When the biomass contains such organic wastes, the amount of residues of the wood industry in this biomass generally comprises between about 25 and about 65%, based on the weight of biomass.